I bought this little box of tricks from the US via Amazon to try to tame my Hot Rod Deluxe. Having sold said HRD within about a week of it arriving it is now surplus to requirements. No idea whether it's classed as an attenuator or a power soak or just a box of heavy voodoo, but it sits in your amp's effects loop to give you a responsive audio taper.
Here's the blurb on Amazon: https://www.amazon.co.uk/Carls-Custom-Guitars-Box-Attenuator/dp/B004ZH0PPY
Used twice. £20 posted.
Self-confessed Blues Lawyer